The invention relates to a method and system for controlling rotary or linear electric drives. More particularly, the invention relates to a system and method for the generation of a partly synthesized signal of high dynamic quality to control the acceleration of an armature (rotary or linear) of an electric drive.
In order to design high-quality position or speed control for a rotary or linear electric drive it has been customary in the past to control the components directly generating torque or force in the innermost loop, that is, in cascade control. The most recent developments have shown that on the other hand it is highly advantageous not to control the torque or force generating components of the current volume indicators indirectly, but to guide the acceleration of the part propelled, that is, in cascade control. In the case of rotary drives this is the spin of the rotor, and in the case of linear drives it is the linear acceleration of the armature. Hence, use of an accelerometer is required for registration of these values.
One type of accelerometer that may be used, for example, is an accelerometer which operates on the Ferraris principle. These types of accelerometers have certain deficiencies though. This type of accelerometer, on the whole, is characterized by a delay in measurement, albeit a small one. Another deficiency is that this accelerometer can never be completely rigidly connected to the place engaged by rotary thrust in the case of a rotary drive, or by linear thrust in the case of a linear drive. The result of these two facts is that loop limit cycles and/or self-excited oscillations are formed in the cascade control loop for the acceleration.
Unless these limit cycles and/or self-excited oscillations are prevented, use of such a cascade control loop is not successful for high-quality position or speed control. A method for suppression of these limit cycles and/or self-excited oscillations in the cascade control loop for acceleration has been proposed for rotary drives. However, this process has the disadvantage that its application is extremely costly and that it reacts with extreme sensitivity to fluctuations in the parameters of the drive. Thus, a need exists for a low cost system and method for cascade controlling the acceleration of an armature of an electric drive that is insensitive to drive fluctuations, and prevents limit cycles and/or self-excited oscillations in the cascade acceleration control loop.
It is therefore an object of the invention to provide a system and method for controlling the acceleration of an armature of an electric drive by generating a high quality acceleration error correction signal z, the system comprising an accelerometer for obtaining a measured armature acceleration value bm, which is equal to the product of a true armature acceleration xcex1, and an acceleration measurement transfer function Fg(p), and means for obtaining a measured acceleration signal, bEm, which is generated from a measured substitute acceleration signal bExc2x7bm and bEm are scaled such that the relationship of bm=xcex1xc2x7Fg(p)=bEmxc2x7Fg(p) is satisfied. The measured armature acceleration signal bm is filtered with a first filter transfer function of FT(p), and the measured acceleration signal bEm is filtered with a second filter transfer function of FH(p). The first and second filter outputs are combined to form the partly synthesized high quality acceleration error correction signal z=bmxc2x7FT(p)+bEmxc2x7FH(p).